Steam Content Research Articles

A Conceptual Framework for Computational Pedagogy in STEAM education: Determinants and perspectives

Computational Pedagogy is an instructional approach based on Computational Science and the Computational Experiment as well as on the CPACK model. Computational Science in Education engages students in computational modeling and simulation technology in alignment with the essential features of Inquiry based teaching and learning approach and the Computational Thinking dimensions (practices and skills). STEAM –content based epistemology- education is connected to Computational Pedagogy through the Computational Experiment leading to a proposed model called ‘Computational STEAM Content Pedagogy’ as a teaching and learning approach which can be implemented in a STEAM holistic interdisciplinary/trans-disciplinary epistemology approach to the curriculum for solving real computational problems.

Impact fragmentation of limestone-based sorbents for calcium looping: The effect of steam and sulphur dioxide

Calcium Looping (CaL) for CO2 capture and utilisation is affected by the presence of SO2 and/or H2O in the flue gases that are processed in the carbonator. The influence regards both the course of carbonation as well as the mechanisms and extent of attrition and fragmentation phenomena to which sorbent particles are exposed in Dual Interconnected Fluidised Beds (DIFB) that are commonly used for this process. Fragmentation by impact has been comparatively less investigated with reference to operating conditions entailing the presence of SO2 and/or H2O. In this study, two high-calcium commercial limestones, similar in chemical composition but different in reactivity, have been subjected to CaL tests in a lab-scale DIFB apparatus in presence of sulphur dioxide and/or steam. Calcination was carried out at 940 °C in an atmosphere containing 70% CO2. Carbonation was carried out at 650 °C in an atmosphere containing 15% CO2. The effect of SO2 and/or H2O was assessed with reference to six carbonation atmospheres, with different concentrations of steam (0 and 10%v) and sulphur dioxide (0, 75 and 1500 ppmv). After ten CaL cycles, the particles were tested ex-situ in an impact test rig, consisting of a duct where samples were entrained in a gas stream at a controlled velocity and impacted against a target. The apparatus was operated at room temperature at various impact velocities (six values from 10 to 45 m/s). The extent and pattern of impact fragmentation was assessed by characterising the particle size distribution of the debris and the fractional mass of generated fragments. Results are discussed in the light of the different sorbent nature and of the CaL FB operating conditions.

The effect of Kaolinite’s structure on migration and release characteristics of sodium under oxy-fuel combustion condition

Studying the adsorption properties of kaolinite on sodium chloride is of great significance for application of high sodium coal, but high concentration of steam in the oxy-fuel combustion atmosphere increases the uncertainty of this process. Moreover, under the corresponding condition, the research on the adsorption properties of sodium of kaolinite after calcination and intercalation-exfoliation is still scarce. Therefore, this paper carried out a study on sodium adsorption characteristics of kaolinite. This work further evaluated H2O influence on its Na retention ability via integrating experimental and DFT computational studies. As the proportion of additive increases, the sodium content in the ash also increases, but after the ratio exceeds 9%, the increase is not obvious. The kaolinite’s adsorption performance on sodium chloride has been significantly improved after the intercalation-exfoliation. In order to confirm this conclusion, this paper also carried out adsorption experiments using pure sodium chloride, and obtained similar results. Variations in the concentration of steam (0–45%) in the atmosphere have a strong effect on the adsorption of sodium chloride on the surface of kaolinite. Moreover, both acceleration and competition effects of H2O on surface-bound Na species were substantiated by DFT calculations·H2O showed a stronger interaction with the dehydroxylated surface, can promptly replenish the missing adsorption sites on the surface due to high temperature. The experimental results show that the dynamic balance can be achieved at 20%. However, H2O and sodium chloride compete with each other on the complete adsorption surface, which reduces the fixation of sodium.

Mechanism and thermodynamic study of solar H2 production on LaFeO3 defected surface: Effect of H2O to H2 conversion ratio and kinetics on optimization of energy conversion efficiency

Owing to favorable water-splitting activity at low concentration of steam, LaFeO3 represents promising solar thermochemical (STC) materials to achieve commercial energy conversion efficiency (ηsolar-to-fuel) of 20%, which is far from reaching up to now. Here we propose possible strategy to improve ηsolar-to-fuel of LaFeO3 via solving the scarcity of its water-splitting kinetic and thermodynamic characteristics. The detailed pathway of water-splitting and H2 production around oxygen vacancy site of LaFeO3 is firstly revealed, where the migration of surface H atom is determined as rate controlling step with activation energy of 147.24 kJ/mol. Then, within the good consistent between our thermodynamic calculations and previous experiments, we find that both reduction and water-splitting steps are endothermic, and the conversion ratio of water to hydrogen should be larger than 10% to ensure ηsolar-to-fuel>20%. In addition, the calculated ηsolar-to-fuel with the consideration of water-splitting kinetics shows that only the isothermal condition of 1400 K is beneficial for increasing ηsolar-to-fuel up to 20%. Our work demonstrates the potential of LaFeO3 in efficient H2 production and provides key metrics for further improvement along the pathway to commercialization.

From O2/CO2 to O2/H2O combustion: The effect of large steam addition on anthracite ignition, burnout and NOx formation

Steam-moderated combustion has been proposed to supress flue gas recycling in oxy-fired units, but the influence of replacing CO2 by H2O has to be deeply studied. In this paper, oxy-fuel combustion of anthracite with large steam addition has been experimentally characterized, and main results are discussed as concerns the influence upon the ignition temperature, the burnout and the NOx formation. The tests have been carried out in an electrically-heated entrained flow reactor for a set of O2/CO2 and O2/H2O/CO2 atmospheres, with steam addition up to 40% vol. The results show that ignition temperature diminishes when steam is added in low rates (maximum decrease of 16 °C), but the trend is reversed for the higher steam concentrations (maximum increase of 18 °C). The effect of steam addition on coal burnout rates is more significant for the 21% vol. O2 atmosphere, with a decrease of 2.2–5.3 percentage points, and almost negligible for the 35% vol. O2. An outstanding reduction of NO specific emissions is detected when adding H2O, with decrements ranging 28–45% compared to the dry conditions. The transition from O2/CO2 combustion to O2/H2O combustion barely affects the anthracite conversion but significantly diminishes NOx formation rates.

Electronic Transport within Proton-Conducting Ceramics and Its Effect on Faradaic Efficiency of High-Temperature Water Electrolysis for Hydrogen Production

Proton conducting ceramics are used as electrolyte materials for protonic ceramic electrolysis cells to produce hydrogen through water electrolysis at high or intermediate temperatures. The widely applied barium-cerium-yttrium-zirconium oxides have been well studied as proton conductors for fuel cell applications, which present a promise in commercialization. In water electrolysis operating conditions electronic leakage within electrolyte can be observed, which reduces the Faradaic efficiency (FE) of hydrogen production. To address this electronic leakage problem, the intrinsic mechanism behind it should be understood. In this work, the defect chemistry in barium cerate and barium zirconate doped with yttrium is comparatively studied in terms of proton, electron and hole defect concentration/conductivity, and respective distribution profile within electrolyte, where electronic and protonic current density are calculated under electrolysis working conditions such as steam concentration, oxygen partial pressure, and over-potential. In addition, the conduction behaviors of three typical proton-conducting ceramics: BaCe0.7Zr0.1Y0.1Yb0.1O3-δ, BaCe0.4Zr0.4Y0.1Yb0.1O3-δ and BaZr0.8Y0.2O3-δ are experimentally investigated under different oxygen partial pressures and temperatures to validate with the prior defect equation derivation. The results indicated that high FE can be achieved under optimized conditions with reduced temperatures, implying numerous research opportunities in materials R&D of protonic ceramic electrochemical cells (PCECs) as well as the feasibility for widespread market adoption.

High-Temperature Co-Electrolysis

High-temperature Solid Oxide Electrolysis Cells (SOECs) possess the unique property to convert carbon dioxide and/or steam with a faradaic efficiency of 1 into carbon monoxide and/or hydrogen, respectively. High-temperature co-electrolysis of steam and carbon dioxide offers a suitable technology to provide 'white' syngas. Syngas, a mixture of hydrogen and carbon monoxide, as well as pure carbon monoxide are used in chemical industry for the synthesis of many basic chemicals as well as synfuels. Using renewable energy sources and the climate gas CO2 the high-temperature CO2 and co-electrolysis technology presents a sustainable alternative to conventional processes. The technology of co-electrolysis allows the adjustment of the H2 to CO ratio required for various down-stream catalytic processes in one step.Investigations of the high-temperature electrolysis of steam or CO2 and the co-electrolysis of a mixture of both in the feed gas were performed on so-called fuel electrode supported cells consisting of a 8mol% yttria stabilized zirconia (8YSZ) electrolyte, a Ni/8YSZ support and fuel electrode and a (La,Sr)(Co,Fe)O3 air electrode. The experiments showed that the performance of the cell during CO2 electrolysis is lower than for steam and co-electrolysis, as is shown in the Figure. The performance can be characterized by the slope of the current-voltage curve, i.e. the area specific resistance (ASR). For the CO2 electrolysis the ASR at 900 °C and 1.5 A·cm-2 amounts to 410 mΩ·cm-2. For steam and co-electrolysis, the ASR values are nearly the same: 245 mΩ·cm-2. The lower performance for CO2 electrolysis is attributed to the slower kinetics of the CO2 reduction reaction compared to the H2O reduction reaction. Similar observations were made in fuel cell operation, in which the CO oxidation reaction is around a factor 5 slower than the H2 oxidation reaction. The similar ASR values for steam and co-electrolysis are attributed to the occurrence of the reverse water gas shift (RWGS) reaction, in which CO2 and H2 react to CO and H2O during co-electrolysis. The slower kinetics of the CO2 reduction reaction are by-passed in the RWGS reaction using the hydrogen generated through the steam reduction.Further experiments were conducted to investigate the role and importance of the RWGS reaction during co-electrolysis. At the boundary to pure CO2 electrolysis, the performance of feed gas mixtures with low steam contents were investigated. First results show a significant increase of the area specific resistance at a reduced (RWGS) equilibrium steam concentration of about 5 %. Above 15 % steam in the feed gas (in the RWGS equilibrium) the ASR is no longer influenced by the feed gas composition and similar to that of pure steam electrolysis. Experimental results are furthermore compared to theoretical calculations of syngas production on a thermodynamic and partially kinetic level. Figure 1

High-Performance Protonic Ceramic Electrochemical Cells for Hydrogen Production and Electricity Generation at Intermediate Temperatures

Achieving energy conversion between electricity power and hydrogen in protonic ceramic electrochemical cells (PCECs) is an emerging and attractive approach to store intermittent renewable energies which can be converted back to electricity in reversible operation. Economically competitive PCEC systems have distinct advantages over conventional oxygen-ion conducting counterpart (O-SOC), but further materials innovation is still needed to improve cell performance at reduced operating temperature (400~600○C), enhance system lifetime and reduce cost. To achieve efficient electrochemical hydrogen and power production with stable operation, highly robust and durable oxygen electrode is urgently desired to facilitate water oxidation and oxygen reduction reactions, which are the critical technical barriers for both electrolysis and fuel cell operation at reduced temperatures. The recent efforts in this study have been focused on developing new triple conducting electrode with perovskite or layered perovskite structure for high-performance and stable PCECs. The systematic material characterizations are carried out to evaluate the feasibility of activity, stability and interface compatibility, such as Fourier-transform infrared spectroscopy, high-temperature X-ray diffraction, hydrogen permeation and first-principal computation. The catalytic activity towards water splitting reaction is demonstrated in various electrochemical performance evaluation at 400~600○C. The long-term durability of the PCEC is examined to show the high resistance against transient current density change in reversible operation and high steam concentration.

Characterization and polarization DRT analysis of direct ethanol solid oxide fuel cells using low fuel partial pressures

Commercial Ni-YSZ anodes of solid oxide fuel cells (SOFCs) are susceptible to carbon deposits using hydrocarbons as fuel. Herein, we explore a simple approach of low fuel partial pressure to investigate the relevant limiting factors for ethanol-fueled SOFCs, providing the evaluation of the electrochemical performance and the carbon tolerance. As the partial pressure of ethanol fuel increases from 30% to 60%, the best cell performance gradually increases from 710.2 mW cm−2 to 856.8 mW cm−2 at 800 °C, which still lower than those of hydrogen-fueled SOFCs (1061.4 mW cm−2 at 800 °C), and the corresponding improvement in concentration polarization can be clearly observed especially in high current discharge area. The corresponding impedance spectra and electrode polarization processes of ethanol-fueled SOFCs are further studied by the equivalent circuit fitting and the distribution function of relaxation time (DRT) analysis, finding that the key improvement of the speed control steps comes from the concentration polarization process with the increase of the fuel partial pressure. Small amount of carbon deposition is observed on the Ni-YSZ anode substrate by SEM-EDS images after short-term discharging testing, and the safety utilization boundaries of ethanol-fueled SOFCs with a certain steam concentration can be predicted by the thermodynamic equilibria calculation.

Effect of steam addition during carbonation, calcination or hydration on re-activation of CaO sorbent for CO2 capture

Calcium looping (CaL), based on cyclic carbonation/calcination using lime-based sorbents, is a promising technology for post-combustion CO2 capture. An important obstacle of this technology is the decay of sorbent over multiple cycles. Steam re-activation is a potential approach to improve the sorbent reactivity, however, the effects of both in-situ high-temperature steam (in carbonator or/and calcinator) and ex-situ low-temperature steam (steam hydration in hydrator) are still a matter of debate. Here, a bubbling fluidised bed reactor was used to investigate three steam addition options: steam addition during carbonation stage, or during calcination stage, or intermediate steam hydration after each CaL cycle. A CaO sorbent was tested under varying steam concentrations up to 40 vol.% for 10 CaL cycles (carbonation: 650 °C, calcination: 900 °C). Compared to the dry condition, steam addition during carbonation and intermediate steam hydration were both found effective for CaO re-activation. For the former, the improved sorbent reactivity was mainly attributed to an increased pore volume enhancing the extent of carbonation in kinetic regime; while for the latter, the formation of cracks accelerated the rate of diffusion. Nevertheless, decreasing the hydration temperature was detrimental to sorbent reactivity due to enhanced sintering upon cooling. In case of steam addition during calcination, the sorbent was affected negatively or positively depending on the concentration of steam. At higher steam concentrations (20, 40 vol.%), the sorbent reactivity was significantly decreased due to sintering associated with larger pores and lower surface areas. Overall, steam addition during carbonation was recommended for sorbent re-activation.

SO2 removal performances of Al- and Mg-modified carbide slags from CO2 capture cycles at calcium looping conditions

In this work, the SO2 removal performances of the aluminum- and the magnesium-modified carbide slags fabricated by the combustion synthesis from CO2 capture cycles at the calcium looping conditions were investigated in a thermogravimetric analyzer and a dual fixed-bed reactor. The effects of sulfation temperature, number of CO2 capture cycles and calcination condition on the SO2 removal performances of Al- and Mg-modified carbide slags experienced the multiple CO2 capture cycles were studied. The sulfation temperature in the range of 800–950 °C shows a little effect on SO2 removal capacities of Al- and Mg-modified carbide slags experienced the multiple CO2 capture cycles. As the number of CO2 capture cycles increases, the sulfation conversions of the original and modified carbide slags decrease rapidly. However, Al- and Mg-modified carbide slags possess obviously higher SO2 removal capacity and cyclic stability than original carbide slag due to the good supports Ca3Al2O6 and MgO, respectively. And the larger surface areas and volumes of pores in 5–20 nm in diameter of Al- and Mg-modified carbide slags promote the higher SO2 removal capacity than original carbide slag. The modified carbide slag shows higher sintering resistance in high concentration of steam calcination condition during the CO2 capture cycles, compared with high concentration of CO2 calcination condition. Therefore, Al- and Mg-modified carbide slags from CO2 capture cycles based on calcium looping calcined under high steam concentration achieve SO2 removal capacities.

CFD modeling on char surface reaction behavior of pulverized coal MILD-oxy combustion: Effects of oxygen and steam

Gasification reaction is not supposed to be omitted for pulverized coal MILD-oxy combustion regime, especially for the wet recycle (steam up to 40 vol%). This paper numerically investigates the individual effects of steam and oxygen on pulverized coal MILD-oxy combustion to have better understanding of char reaction behavior under this combustion mode. Results show that, the flame temperature affected by steam is because of thermal radiation, whereas that of O2 is because of chemical reactivity. The maximum value of the turbulent Damköhler number (Da,t) is within 0.25–1.9 for all cases, implying that the rate of chemical reaction is comparable with that of turbulent flow. For 30% O2 and 40% steam cases, gasification reaction accounts for up to ~62%. With a given O2 level, the reaction of char-H2O competes the active sites with char-O2 and char-CO2, whereas for a certain level of steam, a positive synergy exists between char-H2O and char-CO2. The effect of CO + H2O → CO2 + H2 on generating H2 becomes increasingly significant when O2 content is >21%, and easy to occur under low steam concentration. Increasing the O2 and steam is conducive for the decrease in overall char burnout rate. As the steam content increases, the reduction on char burnout rate is insignificant for 18% and 21% O2 cases, but it is serious for 24%–30% O2 cases.

Surface structure–activity relationships of Cu/ZnGaOX catalysts in low temperature water–gas shift (WGS) reaction for production of hydrogen fuel

A new species’ class of Cu-, Ga- and Zn-based rate catalysts was prepared by a systematic co-precipitation technique at the different related pH values (6.5–8.0) along with calcination functional conditions, influencing components’ physical properties, these were characterized, and their application performance for water–gas shift (WGS) reaction was researched. Substances were analysed by various experimental methods, namely chemisorption, temperature-programmed reduction (TPR) characterisation, diffraction, physisorption and microscopy. A homogenous size dispersion of the compounds with smaller granular particles was obtained for catalysis, implemented with high pH-resulting outputs. H2 TPR profiles revealed a tailored stronger effect of Cu–Zn on Ga for process, operated with low pH-conditioned forms. Over Cu/ZnGaOX, WGS was sensitive to Cu, which was primarily active. Catalytic chemical reactivity, activity and selectivity were also found to be critically dependent on material lattice structure, copper surface area and metal–support interaction phenomena. The temperature-programmed surface reaction with mass spectrometry (TPSR–MS) measurements showed that formulations, synthesised at the pH of 8.0, enabled reaching >99% of the equilibrium yield CO conversion at 260 °C. An increase in the converted CO, oxidation and H2 productivity with the integral steam content in gaseous feed flow was achieved. The heterogeneous phase processing at the correlated pH of 7.6 demonstrated the highest formed CO product at the temperature of 200 °C, compared with literature. This is particularly promising for reagent purity hydrogen-fed fuel cells. The kinetics for each co-precipitated solid was evaluated regarding the efficiency for the WGS in a fixed bed reactor.

Comprehensive Modeling of Sorption-Enhanced Steam Reforming of Coke Oven Gas in a Fluidized Bed Membrane Reactor

Integration of membrane hydrogen separation and carbon dioxide capture with fuel steam reforming efficiently promote hydrogen production and feedstock conversion. In this study, catalytic steam reforming of coven oven gas in a sorption-enhanced fluidized bed membrane reactor (MA-SE-SRCOG) was simulated using a reactive three-fluid model under Euler framework. The numerical studies provided insights into details about interactions of multi-scale sub-processes, including hydrogen permeation, carbon dioxide adsorption, catalytic reforming and multiphase flow dynamics, during MA-SE-SRCOG. Concentration polarization caused by hydrogen separation was also examined. Meanwhile, impacts of several operating parameters, such as reaction pressure, steam concentration, membrane position and reactor scale, on the performances of MA-SE-SRCOG were evaluated in terms of CH4 conversion, CO selectivity, hydrogen recovery factor and CO2 fix factor. The simulation results demonstrated that membrane hydr...

Геотермальные энерготехнологии России

The results of scientific and technical investigations and development of geothermal technologies in Russia are presented. Information on the geothermal resources in Russia, the characteristics of geothermal fields and the physicochemical properties of geothermal fluids is given. The article presents the most significant results from experimental studies and numerical modeling of crisis phenomena in wet steam flows in the zone near the upper boundary curve, the generation and precipitation of a dispersed liquid phase, the flow of liquid films and moisture separation, and the formation of deposits and regularities relating to flow accelerated corrosion of structural metals in a multicomponent geothermal fluid. The article also discusses the design features and advantages of Russian geothermal equipment, including gravity separators, steam turbines with a developed system for intra-channel separation of moisture from the flow path, a cooling system, and a system for reinjection of waste geothermal fluid. It is shown that the use of gravity separators produced by the JSC Machine Building Plant ZiO Podolsk makes it possible to keep the moisture content of steam at the turbine inlet at a level of 0.1-0.5%, thereby significantly reducing the deposit formation rate in the turbine stages. It is also shown that the use of the intra-channel separation system and the steam turbine’s dedicated separation stage makes it possible to remove more than 80% of moisture from the flow path. Basic information about the process flow diagrams, design and technical characteristics of the equipment installed at the operating Russian geothermal power plants, including the Verkhne-Mutnovskaya GeoPP and the Mutnovskaya GeoPP in Kamchatka, is given. Some results from recent studies on achieving more efficient use of the geothermal fluid heat are presented, in particular, through applying a system for superheating steam at the turbine inlet and secondary flashed steam by using hydrogen-oxygen steam generators. Promising sites for constructing new Russian geothermal power plants have been identified.

Hydrogen production of solar-driven steam gasification of sewage sludge in an indirectly irradiated fluidized-bed reactor

A fluidized-bed based solar steam gasification of sewage sludge for production of high-quality syngas with a high content of hydrogen is numerically modeled and validated by experimental data generated from a lab-scale fluidized bed. The solar gasifier is mainly composed of a fluidized bed and a concentrically tubular cavity. A transient model coupling a two-phase fluidization model (in terms of reaction kinetics and hydrodynamics) and a solar cavity receiver model is established to conduct the parametric investigation of the proposed solar gasifier, including the effects of the direct normal irradiance, gasifying agent composition, and spatial flux distribution at the freeboard wall on the performance criteria of solar gasification i.e. solar upgraded ratio and solar-to-fuel efficiency. The transient simulation of the solar gasifier with ~2.2 MW solar power input is performed. A H2 yield range of 61.2–67.6 g/kg(sludge) can be achieved through solar steam gasification of sewage sludge, which can be adjusted by modifying the steam content of the gasifying agent and the direct normal irradiance. Under the condition of the direct normal irradiation of 1000 W/m2, the mean concentration ratio of 1000 suns at the dense bed, and 100 vol% N2 content, a maximum solar upgraded ratio of 1.0 and solar-to-fuel efficiency of 0.26 can be achieved.

Effect of direct-current operation on the electrochemical performance and structural evolution of Ni-YSZ electrodes

The effect of electrolysis operations on Ni-YSZ fuel electrode stability was studied at different current densities and fuel mixtures during 1000 h life tests. For a typical electrolysis mixture of 50% H2/50% H2O and 0.6 A cm−2 current density, cell ohmic resistance values were reasonably stable and no structural changes occurred. However, for more reducing conditions (97% H2/3% H2O), increasing the current density above 0.4 A cm−2 increased the ohmic resistance accompanied by significant electrolyte degradation including fracture and void formation at grain boundaries. Numerical analysis was carried out to determine the effective oxygen partial pressure across the electrolyte. The results show that the oxygen partial pressure values at high current density and low steam content may be low enough to reduce zirconia to form a Ni-Zr alloy product, initiating the observed electrolyte structural degradation.

Promising zirconia-mixed Al-based nitrogen carriers for chemical looping of NH3: Reduced NH3 decomposition and improved NH3 yield

The chemical looping ammonia generation (CLAG) of N-sorption/desorption reactions via Al-based N-carriers for producing ammonia (NH3) (a non-carbon fuel) is thought to be an important alternative to the conventional Haber–Bosh NH3 synthesis technology. However, the low yield of NH3, because of significant NH3 decomposition at the required N-desorption temperature, inhibits the development of CLAG. Accordingly, ZrO2 mixed AlN was designed in this study to investigate the NH3 generation characteristics of AlN during the N-desorption process in a stationary bed reactor. The results showed that ZrO2 can improve the formation of NH3 because the molecular adsorption of NH3 occurred on the ZrO2 surface, thus preventing NH3 from decomposing. The ZrO2 loadings and steam concentrations in the atmosphere positively affect the yield and generation efficiency of NH3, while increasing the reaction temperature increased the NH3 yield from 1.2 to 3.3 mmol, but reduced the NH3 generation efficiency from 91.7% to 60.3%.

A study on the kinetics of bismuth oxide reduction by hydrogen as applied to the technology of removing hydrogen from circulation circuits with heavy liquid metal coolants

As part of the project on developing methods for removing hydrogen and tritium from the circulation circuits of reactor plants with heavy liquid metal coolants, the authors studied the kinetics of bismuth oxide reduction by hydrogen in the temperature range of 425–500 °C and hydrogen concentrations of 25–100 vol.%. The kinetic characteristics of the test reaction were determined by continuous measurements of the water steam (reaction product) concentration in mixtures of hydrogen with helium that passed through a heated reaction vessel with a sample of bismuth oxide. The water steam concentration was measured by a thermal-conductivity detector. The obtained time dependences of the bismuth oxide reduction degree (with varying reaction conditions) were processed by the affine time transformation method. It was also found that the reduction process ran in kinetic mode. The reduction mechanism is the same in the entire temperature range. The limiting reaction stage is the adsorption of hydrogen on the surface of the bismuth oxide sample. The time dependence of the reduction degree is in good agreement with Avrami-Erofeev equation with n = 1. The reaction activation energy is 92.8 ± 1.9 kJ/mol. The reduction reaction rate is directly proportional to the concentration of hydrogen in its mixture with an inert gas.

Robust modeling, analysis and optimization of entrained flow co-gasification of petcoke with coal using combined array design

This study is focused on robust modeling, analysis and optimization of entrained flow co-gasification of petcoke with coal, which is very important to the stable operation of this process as well as downstream processes. Unlike general robust modeling method that traditional Taguchi's crossed array design is applied, combined array design was used in this study. Then based on the exiting general experiments and the constructed robust models, a systematic investigation was conducted into the effects exerted by oxygen and steam concentrations (OC and SC) not only on the mean but also on the variance of H2, CO and (H2 + CO) production. Finally, the co-gasification process was robustly optimized. The result reveals that the average production of H2, as well as that of (H2 + CO), rises with OC increasing but declines with SC increasing. Moreover, higher OC inhibits the fluctuations in H2 and (H2 + CO) production, while higher SC makes their fluctuations more notable. The robust optimization solutions of OC and SC are observed to be 1.56% and 50%, respectively.